THE Tory mutiny over grammar schools deepened yesterday as David Cameron was knifed by David Davis - his main rival for the party leadership.

Davis, the shadow Home Secretary, set himself at odds with Eton-educated Cameron by insisting grammar schools helped boost the chances of children from less welloff backgrounds.

He said: "My primary interest in this is the simple issue of social mobility - making sure youngsters get the best chances.

"Now, there is more than one way to do that. Grammar schools is one - and where they're there we will continue with them."

Davis, a former grammar schoolboy, also pointedly reminded viewers during the interview on the BBC's Sunday AM show that he had backed selective schooling during the 2005 Tory leadership contest - which he lost to Cameron

Davis's intervention will be a bitter blow to Cameron, who is desperately hoping the education row will die down.

The Tory leader insists grammar schools do little to help the least well off. He recently said the best way to improve social mobility was to ensure good standards of discipline and behaviour and then good standards of teaching and learning "in all 24,000 state schools, not just the 166 grammar schools."

But many Conservatives feel they benefitted from a grammar school education and are angry that someone from such a privileged background wants to deny their children a similar opportunity.

Earlier this month, ex-Tory minister David Mellor said: "I just think it's a bit foolish for an old Etonian to appear to want to pull up the ladder of opportunity from ordinary folk."

Cameron's announcement that a Conservative government would build no more grammar schools sparked a widespread revolt within the party - highlighted by the dramatic resignation of his Europe spokesman Graham Brady.

He was then accused of a U-turn after his Education spokesman David Willetts said new grammars might be built in areas where selective schooling already existed, to cope with demand.

As the row has escalated, Cameron has been accused of coming over as panicky and shrill in what is his first real crisis.

In contrast, Davis appeared relaxed about the issue yesterday. He said: "This is three weeks of slightly rough water. So what, frankly?"